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Just Thinking Out Loud Here. Changing Stroke Length....


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#1 nicklouse

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Posted 24 March 2020 - 11:17 PM

If you shorten the stroke for a given piston diameter you reduce the CR.

 

mmm who does shorter stroke cranks now? As I am allowed to go to less than 1300cc



#2 1968andyf

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Posted 24 March 2020 - 11:54 PM

73.5mm bore 76mm stroke gives 1299cc both med and swiftune do steel cranks probably not cheap though, might need 970 rods as well

#3 GraemeC

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Posted 25 March 2020 - 07:11 AM

You could use a 12G2827 SA crank which is about a 70mm stroke but 1.75” big ends so can be offset ground.



#4 mini13

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Posted 25 March 2020 - 12:08 PM

okay, is there some more background here?

 

race reg? why is the CR important?



#5 nicklouse

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Posted 25 March 2020 - 10:32 PM

Just thinking out loud. If the block will not take a hone. And the head can not have CCs added then bore it and short stroke it.

 

out here the limit is 1300cc so 1299 is perfect.

 

and if I am spending 3.5k on crank  rods and pistons anyway......



#6 Moke Spider

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Posted 26 March 2020 - 12:06 AM

Reducing the Stroke will reduce the CR, however, increasing the Bore - on paper - will increase the CR.

In both cases, it depends on the Pin height and also the Crown Shape.



#7 DeadSquare

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Posted 26 March 2020 - 09:16 AM

73.5mm bore 76mm stroke gives 1299cc both med and swiftune do steel cranks probably not cheap though, might need 970 rods as well

 

 

 

The (just over 76mm) 3" stroke 2" mains 998 engine nearly happened. (it could have used an A.H. Sprite Mk4 block),

 

For about two years there was a pile of un-machined forgings in a scrap yard in Wolverhampton, and here is the sad part, they had that EN 40 tell-tale S 'ring' to them.



#8 mini13

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Posted 26 March 2020 - 10:17 AM

Fair enough,

 

also if you cant take meat out of the head, its relativly easy to pop the pistons on a lath and take the dish out, unless youve got an odd dish ( v wedge, valve cutouts etc)

 

 

 

Just thinking out loud. If the block will not take a hone. And the head can not have CCs added then bore it and short stroke it.

 

out here the limit is 1300cc so 1299 is perfect.

 

and if I am spending 3.5k on crank  rods and pistons anyway......

 



#9 nicklouse

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Posted 26 March 2020 - 12:00 PM

 

Fair enough,

 

also if you cant take meat out of the head, its relativly easy to pop the pistons on a lath and take the dish out, unless youve got an odd dish ( v wedge, valve cutouts etc)

 

 

 

Just thinking out loud. If the block will not take a hone. And the head can not have CCs added then bore it and short stroke it.

 

out here the limit is 1300cc so 1299 is perfect.

 

and if I am spending 3.5k on crank  rods and pistons anyway......

 

current S pistons had 8cc new forged Omegas will have 6cc

 

so I am just running ideas through

 

other option is to re-liner it. and work the pistons if possible.



#10 mini13

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Posted 26 March 2020 - 04:09 PM

Liners is another good option.

 

I did see a pic of a KAD engine on facebook, and it looked to have oversize liners in ( not the normal ones, over oversize) it looked like it might be able to take a big bore 73-73.5, rather than the normal linered +20-+40






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